‘Olsen Bosc’ is a new and distinct variety of pear tree (Pyrus communis L.) discovered as a limb mutation of a ‘Bosc’ pear tree (not patented) growing in a cultivated pear orchard near Zillah, Wash. in 2000. Fruit on the mutated limb was observed to be smoother and more russeted than fruit found elsewhere on the tree. After several years of observation, buds from the limb mutation were asexually propagated by grafting at a fruit tree nursery near Quincy, Wash. in 2007. ‘Olsen Bosc’ has since been asexually reproduced and fruited through successive generations at Quincy, Wash., and has been observed to remain true to type.